The present invention concerns an apparatus, a mold and a stopping procedure for horizontal direct chill casting (HDC) of light metals, especially magnesium and magnesium alloys.
Typically, magnesium and magnesium alloys are cast into ingots or billets and delivered to the customers. The ingots formed often have a poor surface quality. In addition this is not an efficient production method. Vertical direct chill casting of billets provides a product with a high surface quality, but continuous production is not possible because the number of strands are limited. There is therefore a need for a process which provides a high quality product which is free from cracks and shrinkage cavities, and can be cast continuously at a high casting speed.
Horizontal direct chill casting is a method that could fulfil these requirements. This process allows the advantages of multistrand continuous casting and also provides a uniform size of product. However, even though this is proven technology for the casting of aluminum and aluminum alloys, it is not a production method used for magnesium ingots today. Many attempts have been made over the course of several years, but there has been problems finding an apparatus and especially molds that can be used. In addition, when working with a reactive metal such as magnesium, the safety aspect is very important and a safe production process is necessary.
British Patent No. 1 194 224 describes a method of horizontally continuously casting ingots of aluminum and magnesium and their alloys. The apparatus includes a reservoir for molten metal which is separated from the mold by a partial barrier (header plate) which does not chill the mold. The header plate has an opening for passage of the liquid metal therethrough and directly into the chilled mold where the metal is solidified and continuously withdrawn in a horizontal direction. Cooling water is discharged from a chamber in the mold wall through channels for directly cooling the emerging ingot. The mold also has a number of channels for supplying lubricant to a peripheral inner surface of the wall.
The apparatus could be useful for casting aluminum but not for the safe production of cast magnesium and magnesium alloys with a good surface finish. The apparatus has a very wide inlet which would result in difficulties regarding control of the solidification process. The mold depth is too large and the cooling system would cause problems in the case of a run-out of metal.